CN104965529A - Large-stroke compound ultra-precision position measurement and control system and method - Google Patents

Abstract

The invention discloses a large-stroke composite ultra-precision position measurement and control system and method, wherein the system includes an alignment platform, a detection and recognition system, a control system and a driving mechanism, and the detection and recognition system includes an image detection and recognition system based on computer vision and a grating-based moire signal detection and recognition system; computer vision-based image detection and recognition system includes CCD, magnifying lens and image acquisition card; grating-based moire signal detection and recognition system includes light emitter, detection grating and photoelectric sensor; control system for image acquisition The image information collected by the card is processed to obtain the position deviation, and the light intensity of the mosaic signal generated by the detection light emitted by the light emitter measured by the photoelectric sensor after passing through the grating is processed to obtain the relative displacement. The invention combines coarse alignment based on image recognition and fine alignment based on grating, proposes a composite ultra-precise position, and realizes high-speed, high-precision alignment of the workbench within a large stroke range.

Description

Large stroke composite ultra-precise position measurement and control system and method

technical field

The invention mainly involves image processing technology in computer vision and signal detection technology in laser cascade signal, and therefore belongs to the technical field of precision measurement and processing.

Background technique

With the rapid development of the market economy, people's expectations for products are not limited to the places that can be observed by the naked eye, but are more deeply developed towards smallness, precision and limit. As one of the mainstream representative technologies, ultra-precise position control is increasingly in demand in the market. It is a highly comprehensive subject, mainly including automatic control, image processing, and precision measurement.

In this era of highly integrated, highly automated, and large-scale electronic information, manufacturers are increasingly demanding the accuracy of alignment devices. For example, a dynamic random access memory (DRAM) with a storage space of 1Gbit has the smallest line width. The value can reach 0.15, and the production process requires that the alignment accuracy of the product needs to reach the minimum line width of 10%, that is, about 15nm. The development status of domestic ultra-precision position measurement and control technology is generally good. In recent years, workbenches with precision reaching the micron level have been developed one after another. There are relatively few ultra-precision worktables with 100 microns and a stroke of tens of millimeters, and the inability to achieve rapid alignment under large strokes. These problems restrict the development of the precision position measurement and control industry.

One of the most prominent contradictions in the process of high-precision position control is how to achieve high-precision and fast alignment under large strokes. Usually, the alignment accuracy varies inversely with the working stroke, and the greater the alignment stroke, the lower the alignment accuracy that the system can achieve. In the process of coarse alignment using computer vision, the system can move on the entire workbench with a large stroke, but the adverse effect is that the accuracy of alignment cannot be improved; in the fine alignment using laser mosaic signals In the process, the system can achieve quite high precision, but only in a limited and small working stroke.

Contents of the invention

The technical problem to be solved by the present invention is to provide a large-stroke composite ultra-precision position detection and control system and method for the above-mentioned deficiencies in the prior art, which solves the inherent gap between alignment stroke and alignment accuracy in precision position control. The contradiction between them, and finally realize the fast and high-precision alignment under the large stroke.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A large-stroke composite precision position measurement and control system, including an alignment table, a detection and identification system, a control system, and a drive mechanism, the alignment table includes an upper alignment plate and a lower alignment plate, and the control system recognizes The detection information obtained by the system is used to control the driving mechanism to realize the alignment of the workbench, and it is characterized in that: the detection and recognition system includes a computer vision-based image detection and recognition system and a grating-based mosaic signal detection and recognition system; The image detection and recognition system based on computer vision includes a CCD, a zoom lens and an image acquisition card, and the grating-based mosaic signal detection and recognition system includes a light emitter, a detection grating and a photoelectric sensor; the control system controls the image The image information collected by the acquisition card is processed to obtain the position deviation between the upper alignment plate and the lower alignment plate, and the mosaic grid generated after the detection light emitted by the light emitter measured by the photoelectric sensor passes through the grating The light intensity of the signal is processed to obtain the relative displacement between the upper alignment plate and the lower alignment plate; the driving mechanism includes a ball screw driving mechanism and a piezoelectric ceramic driving mechanism, and the control system obtains the position according to the processing The deviation controls the ball screw driving mechanism to adjust the alignment table, and the control system controls the piezoelectric ceramic driving mechanism to adjust the alignment table according to the relative displacement obtained through processing.

The grating-based moire signal detection and recognition system includes a coarse grating-based moire signal detection and recognition system and a fine grating-based moire signal detection and recognition system.

The ball screw driving mechanism is driven by a stepping motor.

The grating-based mosaic signal detection and recognition system further includes a preamplifier, a filter and an A/D converter sequentially arranged at the output end of the photoelectric sensor.

The piezoelectric ceramic driver includes piezoelectric ceramics and a high voltage driver.

The control system is an industrial control computer.

An alignment control method based on a large-stroke compound precision position measurement and control system, characterized in that it includes the following steps:

The coarse-precision position measurement and control part of image recognition and analysis using computer vision: CCD and magnifying lens are used to collect images of the original position of the alignment plate, and the control system recognizes and analyzes the processed image data to obtain the relative position deviation of the object to be measured , so as to give a pulse command to drive the alignment table to align the longitude and latitude in micron-level coarse precision alignment;

The precision position measurement and control part of light intensity detection by using laser mosaic signal: the control device is composed of two sets of diffraction gratings, and a set of anti-phase 0 laser mosaic signals are obtained during the control process, and the photoelectric sensor is used to measure the mosaic signal. The relative displacement obtained by the light intensity is issued by the control system to make the worktable move to the error zone, and finally complete the precise position control.

The precise position measurement and control part of light intensity detection using laser cascading signals includes a coarse grating alignment step and a fine grating alignment step, and the coarse grating alignment step makes the workbench enter within a specified error range. At this time, the control According to the magnitude and direction of the mosaic signal value obtained under the fine grating structure, the system sends instructions to the piezoelectric ceramic micro-displacement device to drive the worktable to move, and finally realizes the alignment accuracy of nanometer-level ultra-precision alignment.

Compared with the prior art, the three-stage compound control technology proposed by the present invention, which combines the rough alignment of image processing with the fine alignment of coarse and fine grating detection, can effectively improve the The precision of system control, combined with speed and precision at the same time, ensures the accuracy of system alignment and greatly improves the speed of system alignment.

Description of drawings

Figure 1 is a block diagram of the system as a whole.

Figure 2 is a schematic diagram of image coarse alignment.

Figure 3 (a) and (b) are the results of crosshair and mesh detection in computer vision detection, respectively.

(a) in FIG. 4 is a schematic diagram of an anti-phase differential double grating used in the present invention, and (b) is an experimental graph of a differential mosaic signal.

Fig. 5 is a schematic diagram of the alignment of the combination of coarse and fine gratings.

Figure 6 shows the final experimental results of the system under large-travel compound alignment control, where (a) is the alignment result achieved in the fine alignment environment of the coarse grating, and (b) is the ultra-precision alignment environment of the fine grating The alignment results achieved below.

Detailed ways

The overall structural block diagram of the alignment table is shown in Figure 1 below, and it is mainly composed of the following parts: computer vision detection part, laser detection part, sensor, stepping motor drive mechanism, piezoelectric ceramic drive mechanism, industrial control computer, etc. The operation has formed a large-stroke composite high-precision position measurement and control system.

Position control using computer vision belongs to the stage of coarse-precision position control. The CCD and the magnifying lens can move horizontally, vertically and rotationally along the screen. These three movement modes respectively represent the movement in three directions in space. Among them, the rotary motion is driven and controlled by the pulse subdivision stepper motor, and the worm gear is used to convert the subdivided motor rotation angle into the rotation angle of the alignment mechanism; and the linear motion also uses pulse subdivision A high-precision stepping motor is used for drive control. In addition, under the action of the precision screw mechanism, the fine angle generated by the subdivided motor is converted into the corresponding displacement. During this process, the resolution of rotation angle and linear displacement can reach 1.8 and 0.3 respectively.

The position control using the laser mosaic signal belongs to the stage of precision and ultra-precision position control, which is based on the coarse alignment of the first stage. Since the coarse alignment mechanism has a large alignment stroke, the micro-displacement driver can Further realize high-precision alignment on a larger alignment stroke, which well compensates for alignment errors caused by excessive alignment strokes, and greatly improves the displacement resolution of the system. The driving mechanism used in ultra-precision position control is piezoelectric ceramics. Compared with other driving mechanisms, piezoelectric ceramic micro-displacement drivers have the advantages of extremely high resolution, no stick-slip phenomenon, small size, and fast response speed. It is very suitable as a driving mechanism in ultra-precision control. The piezoelectric workbench is mainly composed of stacked piezoelectric ceramics and flexible hinges. Like the coarse motion table, it can realize free displacement movement in three directions. At this time, the movable range of the micro motion table is 25, and the linear and angular displacement resolutions are respectively is 2.

In the present invention, the realization of ultra-precise position control needs to go through three links, which are respectively: coarse and precise position control based on machine vision, precise position control based on coarse grating, and ultra-precise position control based on fine grating. Each link is specific Proceed as follows:

(1) Coarse and precise position control: the coarse and precise position control method using computer vision for image recognition and detection, the CCD and the magnifying lens are used to collect images of the original position of the alignment plate, and the computer recognizes and analyzes the processed image data, The relative position deviation of the object to be measured is obtained, so as to give a pulse command, and drive the workbench to perform coarse-precision alignment. At this time, the alignment accuracy of the worktable can reach ±500 μm, and the corresponding working stroke can reach 60 mm.

In order to better improve the resolution of the object to be measured and pave the way for fine alignment, the Canny operator is selected for edge detection during image processing, and the initial image captured by the CCD is preprocessed, where the Gaussian variance is 1, The convolution kernel is 5. After extracting the edge information of the image, the XOR method is used to perform cross-hair detection and mesh detection respectively, and the detection results are shown in Figure 3 (a) and (b).

(2) Precise position control: After the rough alignment of the image, the system enters the moving range of the coarse grating, and the grating constant of the coarse grating is set to 1000. There is a relationship between the change of the laser light intensity after diffraction and the relative position between the two gratings. Periodic changes, especially when the light intensity changes close to the alignment point, the change curve is almost linear. According to this rule, the corresponding position information can be mapped out by determining the laser light intensity. When the computer receives the position After the deviation, a control pulse is quickly sent to the drive mechanism to make the drive mechanism move to eliminate the error, and finally realize precise position control.

In the precise position control process, the relative positions of the two sets of gratings used in the present invention are not strictly aligned, but separated, as shown in Figure 4(a). The reason why two sets of gratings with completely opposite phases are set is because the control signal of the system takes the difference between the two sets of signals, which becomes twice the original signal, which greatly improves the sensitivity of the mosaic signal. Figure 4(b) The middle is the control signal of the system in the fine alignment link, that is, the differential mosaic signal. At that time, the differential signal is 0, and the intersection point at this time is set as the alignment point to be detected. When changes occur, they also change periodically. During the control process, keep one of the two gratings still, and send control commands to the corresponding drive mechanism according to the magnitude and polarity of the differential mosaic signal obtained by computer analysis, and the other grating will be moved and adjusted so that it can be controlled at within the vicinity of the alignment point. The alignment stroke of the workbench in this link can reach 1000, and the alignment accuracy can reach. The experimental curve is shown in Figure 6 (a).

(3) Ultra-precise position control: On the basis of the coarse grating position control in the previous step, the fine grating is used for the next ultra-precise position control. At this time, the grating constant is set to 25, and the whole system uses the industrial control computer as the core to work The stage performs real-time closed-loop control, and the computer determines the instruction according to the magnitude and direction of the mosaic signal, and drives the alignment stage to move to eliminate errors. After three links, the alignment accuracy that the workbench can achieve is ±10. The experimental curve results are shown in Fig. 6(b).

After large-stroke composite ultra-precise position detection and control, the present invention enables the workbench to realize high-speed ultra-precise position control within a relatively large stroke.

Claims (8)

1. A large-stroke compound precision position measurement and control system, comprising an alignment platform, a detection and identification system, a control system and a drive mechanism, the alignment platform includes an upper alignment plate and a lower alignment plate, and the control system is based on the described The detection information obtained by the detection and recognition system is used to control the driving mechanism to realize the alignment of the workbench, and it is characterized in that: the detection and recognition system includes an image detection and recognition system based on computer vision and a grating-based mosaic signal detection and recognition system; the image detection and recognition system based on computer vision includes a CCD, a zoom lens and an image acquisition card, and the grating-based mosaic signal detection and recognition system includes a light emitter, a detection grating and a photoelectric sensor; the control system, for the The image information collected by the image acquisition card is processed to obtain the position deviation between the upper alignment plate and the lower alignment plate, and the detection light emitted by the light emitter measured by the photoelectric sensor is generated after passing through the grating The light intensity of the mosaic signal is processed to obtain the relative displacement between the upper alignment plate and the lower alignment plate; the driving mechanism includes a ball screw driving mechanism and a piezoelectric ceramic driving mechanism, and the control system is based on the processed obtained The position deviation controls the ball screw drive mechanism to adjust the alignment table, and the control system controls the piezoelectric ceramic drive mechanism to adjust the alignment table according to the relative displacement obtained through processing. 2. The large-stroke complex precision position measurement and control system according to claim 1, characterized in that: the grating-based moire signal detection and identification system includes a coarse grating-based moire signal detection and recognition system and a fine grating-based moire signal detection and recognition system Signal detection and identification system. 3. The long-stroke complex precision position measurement and control system according to claim 1, wherein the ball screw driving mechanism is driven by a stepping motor. 4. The large-stroke complex precision position measurement and control system according to claim 1, wherein the grating-based mosaic signal detection and identification system also includes a preamplifier, a filter, and a filter arranged at the output end of the photoelectric sensor in sequence. A/D converter. 5. The long-stroke complex precision position measurement and control system according to claim 1, wherein the piezoelectric ceramic driver includes a piezoelectric ceramic driver and a high-voltage driver. 6. The long-stroke complex precision position measurement and control system according to claim 1, characterized in that: the control system is an industrial control computer. 7. An alignment control method based on the large-stroke compound precision position measurement and control system according to claim 1, characterized in that it comprises the following steps: The rough and precise position measurement and control part of image recognition and analysis using computer vision: CCD and magnifying lens collect images of the original position of the alignment plate, and the control system recognizes and analyzes the processed image data to obtain the relative position deviation of the object to be measured , so as to give a pulse command to drive the alignment stage to perform coarse-precision alignment with an alignment accuracy of micron level; The precision position measurement and control part of light intensity detection by using laser mosaic signal: the control device is composed of two sets of diffraction gratings, and a set of anti-phase 0 laser mosaic signals are obtained during the control process, and the photoelectric sensor is used to measure the mosaic signal. The relative displacement obtained by the light intensity is issued by the control system to make the worktable move to the error zone, and finally complete the precise position control. 8. The alignment control method according to claim 7, characterized in that, the precise position measurement and control part using the laser mosaic signal for light intensity detection includes a coarse grating alignment step and a fine grating alignment step, the coarse grating alignment step The grating alignment step makes the workbench enter the specified error range. At this time, the control system sends instructions to the piezoelectric ceramic micro-displacement device according to the magnitude and direction of the mosaic signal value obtained under the fine grating structure, and drives the workbench to move. The final alignment accuracy is nanometer-level ultra-precise alignment.